Inorganic Nitrogen Nutrition Enhances Osmotic Stress Tolerance in Phaseolus vulgaris: Lessons from a Drought-sensitive Cultivar

The nitrogen (N) requirement of legumes can be met by inorganic N assimilation and symbiotic N-2 fixation. Both N assimilation routes have diverse influences on drought tolerance because of the differences in the use of energy and the reduction in power characteristics of those pathways. We investigated N nutrition under osmotic stress and likely criteria conferring tolerance to osmotic stress in common bean. Osmotic stress tolerance in a drought-sensitive common bean cultivar (Coco blanc) was compared with beans relying on N nutrition, N-2 fixation, or fertilization with urea. Osmotic stress was applied by means of 25 (mild stress), 50 (moderate stress), or 75 (severe stress) ram mannitol for 15 days. At the end of the stress period, relative water content, total N contents, total soluble sugars, total chlorophyll, total protein, and potassium were assayed. Urea-fed plants grew better and had better tolerance to osmotic stress. This was attributed to maintaining higher N use efficiency, better leaf hydration, and adequate osmoregulation.